Atherosclerosis is a disease that affects arteries of the body, with most cases affecting the coronary arteries. During the onset of atherosclerosis, changes in the walls of the arteries are seen characterized by increases in cholesterol content and scar tissue. Later on, atherosclerotic plaques build up and thicken the wall of the artery, often causing arterial narrowing artery resulting in reduced blood flow. At these later stages, calcium can be present in the plaques.
As a general matter, it is desired to treat patients found to have plaques because, whether the plaque impedes blood flow or not, their presence presents a risk of rupture which could trigger a coronary event. A ruptured plaque can stimulates local formation of a blood clot that can block the flow of blood to the heart muscle and cause myocardial infarction.